Reverse genetic analyses of gamete-enriched genes revealed a novel regulator of the cAMP signaling pathway in Dictyostelium discoideum

Sexual development in Dictyostelium discoideum is initiated by the fusion of opposite mating type cells to form zygote giant cells, which subsequently gather and phagocytose surrounding cells for nutrition to form macrocysts. Here we performed the targeting of 24 highly gamete-enriched genes we previously isolated, and successfully generated knockout mutants for 16 genes and RNAi mutants for 20 genes including 6 genes without disruptants. In the knockout mutants of two genes, cell aggregation toward the giant cells was much less extensive and many cells remained around poorly formed macrocysts. We named these genes tmcB and tmcC. Although macrocyst formation of wild type cells was suppressed by the addition of exogenous cAMP, that of knockout mutants of tmcB was much less sensitive. The mRNA level of phosphodiesterase (pde) was higher and that of its inhibitor (pdi) was lower in the latter cells compared to the parental strains during sexual development. Thus, tmcB appeared to be a novel regulator of the cAMP signaling pathway specific to sexual development. Knockout mutants of tmcC were indistinguishable from the wild type cells with respect to the cAMP response, suggesting that this gene is relevant to other processes.